Babies' Weak Immune Systems Let In "Good" Bacteria

As any new parent knows, infants are notoriously susceptible to bacterial infections. A study now suggests that the body engineers this vulnerability deliberately, allowing beneficial microbes to colonize the baby’s gut, skin, mouth and lungs. Learning to manipulate this system could lead to treatments for infections in newborns, and perhaps even improve the way babies are vaccinated.

In the womb, a fetus is sterile. But from the moment that a baby travels down the birth canal, bacteria and fungi begin their colonization. How the immune system tolerates this sudden influx of invaders has been a mystery.